Yarn brake for looms

ABSTRACT

A yarn brake includes a fixed frame, fixed and spaced-apart yarn guide elements defining together a straight yarn path through the yarn brake, a rotation drive, and at least one braking element projecting from the rotation drive beyond the straight yarn path. The braking element is controlled by the rotation drive to move through an angular stroke about a rotation axis that is spaced from and essentially parallel to the straight yarn path. The angular stroke has a starting position on one side of the path and a braking position on the other side of the path. An adjustment device varies the degree of deviation of the yarn by varying the braking position of the braking element. The distance between the rotation axis of the braking element and the straight yarn path is variable.

BACKGROUND OF THE INVENTION

The present invention relates to a yarn brake for use in weavingmachines.

A yarn brake--as known from EP-A-326784 by Loepfe--comprises, inaddition to the two fixed yarn guide elements, a swiveling bridgesupporting two further yarn guide elements, aligned with the straightyarn path in the starting position of four rod-shaped braking elements.A certain distance is set between the rotation axis of the brakingelements and the straight yarn path. The bridge rotates about a furtherrotation axis, essentially parallel to and spaced from the straight yarnpath. The bridge is resiliently biased against the braking elements, inits swiveling direction, by repelling magnets positioned into the frame.As the brake is operated, the braking elements are caused to perform anangular movement about their rotation axis from the starting position,laterally across the straight yarn path, into the braking position onthe other side of said path. Due to the tension produced in the yarn,deviated by the braking elements and by the fixed yarn guide elements,the bridge yields with a certain stroke against the force of therepelling magnets. The adjustment device allows to vary the position ofthe repelling magnets inside the frame, so as to vary the counter-forceof the bridge and to thereby vary the degree of yarn deviation and thebraking force acting on the moving yarn.

Another yarn brake--as known from EP-A-527510 by Picanol--provides forthe rotation axis of the two rod-shaped braking elements to bepositioned perpendicularly to the straight yarn path and to intersectsaid path. Both braking elements are positioned on a rotatable diskcontrolled by a rotation drive. The angular stroke of the brakingelements about the rotation axis is limited by taps supported by theframe. The angular position of the taps is adjustable about the rotationaxis of the braking elements through a set of screws engaging into aring supporting the taps inside the frame. Adjusting the angularposition of the taps requires a change in the angular stroke of therotatable disk and of the rotation drive.

A similar yarn brake--known from U.S. Pat. No. 3,406,832 by Rempei--isprovided with two spaced apart stop devices of the frame, whichinterfere with the oscillating path of a lever projecting sideways fromthe rotatable body carrying the braking elements. Two cables, fixed toopposite sides of the lever, are connected with drawing magnetsoperating the rotatable body in both rotating directions. The stopdevices of the frame are thus apt to reduce the maximum angular strokeof the rotatable body. It is possible to vary the degree of yarndeviation in the braking position of the braking elements by adjustingthe stroke of the drawing magnets.

SUMMARY OF THE INVENTION

The object of the present invention is to supply a yarn brake thateasily, but efficiently, varies the degree of yarn deviation in thebraking position of the braking element with a simple structural designof the yarn brake.

Any variation of the distance between the rotation axis of the brakingelement and the straight yarn path is apt to vary the degree of yarndeviation in the braking position of said braking element. This can beobtained, either by moving said rotation axis closer to the straightyarn path or even further from said path, or by moving the straight yarnpath closer to or further from said rotation axis, or finally, byreciprocally shifting both the rotation axis and the straight yarn path.It is anyhow appropriate to merely shift the rotation axis in respect ofthe straight yarn path, as the yarn brake is usually mounted in apredetermined position (defined by fixed yarn guide elements of theframe) in respect of the straight yarn path, aligned with adjacentstructural components forming part of yarn processing system, forexample a weft yarn feeder and the weft yarn insertion means of a loom.

In a further embodiment, the adjustment device shift the rotation axisof the braking element in respect of the straight yarn path.

Another embodiment achieves a simple structure design, in that theamplitude of the angular stroke of the braking element, between itsstarting position and the braking positions, remains unvariedindependently from the selected distance between the rotation axis andthe straight yarn path. With a same angular stroke of the brakingelement it is possible to obtain different degrees of yarn deviation inthe braking position of the braking elements, by varying the length ofthe active lever arm of the braking element, i.e. the distance betweenthe rotation axis and the contact point with which the braking elementengages the yarn to cause its deviation. A constant rotary motion allowsto use a simple rotation drive. Furthermore, the operating stroke of therotation drive can be made to exactly correspond to the angular stroke.

Yet another embodiment achieves an even simpler structural design bymounting the stop devices, which define the starting position and thebraking position, in fixed positions. The stop devices are apt to limitthe angular motion of the braking element or of the rotation drive.

In yet a further embodiment, the braking element directly bears againstthe stop devices, which allows stopping the yarn brake without producingany vibrations; the stopping action is efficiently supported by theresiliency of the material used for the stop devices.

Still a further embodiment is particularly important and involves greatstructural simplicity. To vary the degree of yarn deviation, thestructural unit is mounted on the frame. Any adjustments can be easilycarried out. Suitable positions of the unit can be reset in a precisemanner. The angular stroke of the braking element, between its startingposition and the braking position, may remain unvaried.

In yet a further embodiment the yarn deviation degree can be varied byvarying the distance between the stop devices and the rotation axis ofthe braking element. On the other hand, the adjustment of the stopdevices can for example be used to correct the yarn deviation degree inthe event that only a few and roughly distributed positions to adjustthe rotation axis should be provided.

A further embodiment realizes a simple and reliable structural design.The U-shaped bracket constitutes two simultaneously acting brakeelements. Advantageously, the rotation drive or its shell are apt tosupport the stop devices. The unit is connected to the frame through theshell of the rotation drive or a support thereof. By mounting the unitinto a cut-out section of the frame, one obtains a compactness in theoverall dimensions of the yarn brake.

Another embodiment varies the length of the projecting part of thebraking element, so as to obtain a minimum counter-torque of the mass ofthe braking element on the drive shaft.

The in another embodiment the shape of the braking element isadvantageous in view to minimum moving masses. Furthermore, the slantingcrossbar interconnecting the two arms of the U-shaped bracket preventsthe yarn from getting caught around the braking element, which couldotherwise occur, for instance with highly twisted yarns.

A simple structural design of the frame and an easy adjustment of thedegree of yarn deviation is provided by a further embodiment.

Still another embodiment allows to preset different positions of theunit in the frame, representing different degrees of yarn deviation.

Yet another embodiment conveniently varies the degree of yarn deviation.The adjusting screw allows a fine gradual change of the position of theunit in the frame. The releasable fastening means are apt to firmlysecure the unit to the frame in the instantly selected position ofadjustment.

Another embodiment is advantageous for an efficient yarn braking, withmany points of deviation. The third yarn guide element is aligned withthe other two fixed yarn guide elements.

The, the yarn brake has a compact overall dimension with a structure ofreduced weight in still a further embodiment. The yarn guide elementsand the components for the support thereof do not interfere with themovement of the braking element.

In a further variation, the structural design has the advantage toprevent yarn stops.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail, with reference tosome preferred embodiments thereof illustrated by way of example on theaccompanying drawings, in which:

FIG. 1 is a diagrammatic perspective view of a yarn brake according tothe invention;

FIGS. 2 and 3 are diagrammatic front views of a concise embodiment ofthe yarn brake in two different working positions;

FIG. 4 is a side view of the yarn brake of FIGS. 2 and 3; and

FIG. 5 is a top view of the yarn brake of FIGS. 2 to 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As known, in yarn processing systems, yarn brakes are frequently adoptedto either produce a tension in the yarn, or control yarn tension, orelse slow down the movement of the yarn. An example of yarn processingsystem is represented by a loom, to which there are associated weft yarnfeeding devices. The yarn, withdrawn from the feeding device byinsertion means forming part of the loom, needs--under certaincircumstances--to be braked according to the weaving cycle, i.e. duringeach insertion, in a controlled manner, with a varying braking effect.The so-called yarn deviation brakes have proved their effectiveness inensuring such a controlled yarn braking. When deviating a yarn from itsstraight path, the braking action on the yarn is determined by thefriction forces and by the angles of deviation at the points where theyarn is deviated in respect of the yarn guide elements, which points arecreated for the purpose by the braking element of the yarn brake. Theangle of deviation influences the braking effect according to anexponential function. Consequently, the variations in the angle ofdeviation (or degree of deviation) are an effective measure to preciselyvary the braking action in a wide range.

At certain times, during each weft insertion, any braking effect orfriction influence on the yarn is detrimental and undesirable.

Due to such requirements and to the short time taken for each weftinsertion in modern looms, i.e. less than a second, it becomes essentialto adopt controlled yarn brakes which are extremely reliable and have aquick response. The prevailing influence on the braking effect of theangle of deviation is a useful parameter to vary the braking effect (forexample, for different yarn qualities and different speed conditions).

The described embodiments of yarn brakes involve yarn deviation brakeswherein the degree of yarn deviation can be varied upon request. Thebraking element provided is moved into its braking position with adriving force higher than the counterforce of the yarn, and it is keptin the braking position for the whole time required to brake the yarn.In any case, said brakes can be controlled by varying the action forceof the braking elements so that the yarn itself is, at least partially,apt to move back the braking element from its braking position in thedirection towards its starting position.

The yarn brake B, illustrated in FIG. 1, comprises a frame 1 (orgenerally a fixed support to mount the brake thereon) carrying fixedyarn guide elements 2 and 3 defining together a straight yarn path Calong which a yarn Y extends, in free conditions, through the yarn brakeB. The yarn guide elements 2 and 3 include annular yarn eyelets. On theframe 1 there is mounted a rotation drive D, the rotation axis X ofwhich is essentially parallel to and spaced from the straight yarn pathC. The rotation drive D causes at least one braking element E to performan angular stroke between a starting position (continuous lines inFIG. 1) and at least one braking position E1 (dashed lines in FIG. 1).In the embodiment of FIG. 1, the braking element E is shaped as a rodand it extends from the axis X beyond the straight yarn path C. In thestarting position, the braking element E is placed on one side of thestraight yarn path C. To brake the yarn Y the braking element E moves,with an angular stroke 10, to the other side of the straight yarn pathC, drawing the yarn therewith and causing its deviation in three points,i.e. in correspondence of the yarn guide eyelet 2, about the brakingelement in the braking position E1, and in correspondence of the otheryarn guide eyelet 3. The degree of yarn deviation is indicated by F anddetermines the braking effect of the yarn brake B. The distance betweenthe axis X and the straight yarn path C is indicated by L and can bevaried by means of an adjustment device A incorporated in the structureof the yarn brake B. By varying the distance L (and with a given angularstroke 10 of the braking element E about the axis X), the degree F ofyarn deviation is automatically varied, since the active lever arm ofthe yarn contacting point of the braking element E is accordinglyvaried.

The angular stroke 10 of the braking element E is limited by twoseparate stop devices 4 and 5, engaging the braking element E in itsstarting position and, respectively, in its braking position (E1). Inthe embodiment of FIG. 1, both stop devices 4 and 5 are mounted on therotation drive D; however, such stop devices could alternatively bemounted directly on the frame 1.

In the embodiment illustrated in FIG. 1, the rotation drive D, the stopdevices 4 and 5, and the braking element E, define a structural unit Uwhich is movable inside the frame 1, in respect of the straight yarnpath C, in the direction of the double arrow 9 so as to vary thedistance L. For example, the rotation drive D is positioned in a cut-outsection 6 of the frame 1 and can be shifted in the direction of thedouble arrow 9 by means of the adjustment device A. This can be obtainedby any support means allowing to selectively position the unit U indifferent positions in respect of the frame 1 and of the straight yarnpath C. In this embodiment, at least one adjusting screw 7--penetratinginto the frame 1 and engaging into a flange 8 of the rotation driveD--allows to shift the unit U, either upwards or downwards, and tofirmly secure it to the frame in each selected position. Since the stopdevices 4 and 5 are shifted together with the rotation drive D in theunit U, the angular stroke 10 of the braking element E remains unvariedindependently from the starting position of the unit U within theadjustment range.

The concise embodiment illustrated in FIGS. 2 to 5 represents a compactyarn brake structure, comprising a generally U-shaped frame 1 to fix theyarn brake B onto a structural support component 21 which, for example,carries the upstream yarn guide element 2 of the yarn brake B. The frame1 is firmly secured to the component 21 thanks to the clamping action offastening screws 31 (FIG. 5). The frame 1 carries a U-shaped support 11holding the downstream yarn guide element 3--an annular ceramic yarneyelet--by way of a cover part 12 which fully surrounds the yarn eyelet3 and has rounded or smoothed joints of connection to the support 11. Athird yarn guide element 22 is provided between the yarn guide elements2 and 3, in alignment therewith, said element 22 being supported by acolumn 32 projecting into the support 11.

The frame 1 comprises two essentially parallel sidewalls 14, apt todefine a cut-out section 16 which houses the rotation drive D by way ofits shell 13; the shell 13 has an at least partially rectangular contourwhich fits between the frame sidewalls 14, apt to define a sliding guide15 for the rotation drive D. The stop devices 4 and 5--consisting ofpairs of elastomeric or rubber blocks 17--are fixed to the shell 13 ofthe rotation drive D by means of supporting columns 18. The drive shaft19 of the rotation drive D, coaxial to the rotation axis X of thebraking element E, carries a clamping sleeve 20 having screws 23 toconnect the braking element E with the rotation drive D.

In the embodiments of FIGS. 2 to 5, the braking element E consists of agenerally U-shaped bracket 24, for instance of steel wire, havingparallel arms 25 and 26 and an interconnecting crossbar 27. The arms 25and 26 are of different length, the arm 25 being longer than the arm 26,so that the crossbar 27 extends obliquely with respect to the straightyarn path C. The projecting length of the braking element E from theclamping sleeve 20 can be adjusted, if required, by means of the screws23.

At least one sidewall 14 of the frame 1 is provided with a plurality ofholes 28 to house a fastening screw 29 engaging into the shell 13 of therotation drive D. By unscrewing the screw 29 from the shell 13--from thecounterbore 30 therein--and shifting upwards the rotation drive D fromits lowest position (FIG. 2) to a higher position (FIG. 3) in thecut-out section 16, and by inserting the fastening screw 29 into anotherhole 28 of the sidewall 14, the distance L is reduced to L1 so as toobtain a lower degree of yarn deviation.

Alternatively, instead of providing the holes 28 in one of the sidewalls14, such holes could be formed into the shell 13. It would equally bepossible to provide for more than two different positions of adjustment.Likewise, a longitudinally extending slit could be provided, to allowcontinuously adjusting the position of the rotation drive D. As analternative, or in addition, an adjusting screw 33 could be providedinto at least one of the sidewalls 14 (FIG. 2), to simplify adjustingthe position of the rotation drive D in respect of the frame 1 (steplessadjustment). Furthermore, the frame sidewalls 14 could be provided withlongitudinally extending inner grooves, to guide corresponding flangesprovided on the shell 13, so as to improve the guiding of the rotationdrive D along the frame 1.

For what concerns the rotation drive D, it may consist of a rotarymagnet, of a stepping motor or of a solenoid. If--as shown--the angularstroke 10 remains unvaried, the rotary magnet or stepping motor can beexactly preset for the angular stroke 10. In case the rotation drive Dis operating in a single direction, spring means (not shown) can beprovided to return the braking element E in the non-operating directionof the rotation drive D. Such spring means could either cooperatedirectly with the braking element E, or they could be mounted inside therotation drive D to return also the drive shaft 19. Advantageously, therotation drive D--particularly a rotary magnet M--is adapted forbi-directional operation and can be controlled in both directions. Noreturn spring is thus required.

Thanks to the fact that the axis X of the rotation drive D is parallelto the straight yarn path C, and to the fact that the axial extensionsof the stop devices 4 and 5, the clamping sleeve 20, and the fixed yarnguide elements 2, 22 and 3, all correspond to one another, it ispossible to obtain a yarn brake B of compact overall dimensions. Theyarn brake B can be mounted in any position, namely with the brakingelement E turning upwards (as shown), or else downwardly projecting fromthe drive shaft 19. In order to exclude as far as possible the influenceof the gravity force, the braking element E should be arranged in such away that its starting and braking positions are essentially symmetricalin respect of a vertical plane containing the drive shaft 19 and thestraight yarn path C. The possibility to adjust the projecting length ofthe braking element E is an optional feature of the yarn brake B, whichcan also be omitted.

What is claimed is:
 1. A yarn brake comprising:a fixed frame; fixed andspaced apart first and second yarn guide elements that together define astraight yarn path through the yarn brake; a rotation drive; at leastone braking element projecting from said rotation drive beyond thestraight yarn path, said at least one braking element being moved bysaid rotation drive in an angular stroke about a rotation axis that isspaced from and substantially parallel to the straight yarn path, theangular stroke having a starting position on one side of the straightyarn path and a braking position on an opposite side of the straightline path; and an adjustment device that varies a deviation of yarn fromthe straight line path when said at least one braking element is in thebraking position, wherein a first distance between the rotation axis andthe straight yarn path is variable.
 2. The yarn brake of claim 1,wherein said adjustment device shifts the rotation axis relative to thestraight line path.
 3. The yarn brake of claim 1, wherein the angularstroke has a fixed amplitude regardless of the first distance.
 4. Theyarn brake of claim 1, further comprising a first stop device thatdefines the braking position.
 5. The yarn brake of claim 4, furthercomprising a second stop device that defines the starting position. 6.The yarn brake of claim 4, wherein said first stop device comprises aresilient block in a motion path of said braking element.
 7. The yarnbrake of claim 4, wherein said rotation drive, said at least one brakingelement, and said first stop device together define one structural unitof the yarn brake, and wherein said one structural unit is movablymounted on said fixed frame so as to be movable relative to the straightyarn path.
 8. The yarn brake of claim 4, wherein said first stop deviceis movable relative to the rotation axis.
 9. The yarn brake of claim 4,whereinsaid rotation drive comprises a rotary magnet having a shell anda drive shaft that is substantially parallel to the straight yarn path,said at least one braking element comprises a generally U-shaped bracketwith arms whose ends are fixed to said drive shaft and whose closed endextends beyond the straight yarn path, said first stop device is carriedby said shell, and one of said shell and a support therefor is movablyhoused in a cut-out section of said fixed frame.
 10. The yarn brake ofclaim 9, further comprising a releasable clamp on said drive shaft thatholds said arms of said braking element, said releasable clampcomprising at least one clamping element for selectively adjusting aposition at which said arms are held.
 11. The yarn brake of claim 9,wherein an upstream one of said arms of said at least one brakingelement is longer than a downstream one of said arms, and wherein saidclosed end of said at least one braking element comprises a straightcrossbar that is oblique to the straight yarn path.
 12. The yarn brakeof claim 9, wherein said cut-out section of said fixed frame is definedby two spaced apart sidewalls of said fixed frame that together define asliding guide for said shell, and wherein said shell comprises an outerrectangular portion slidably fitted between said two sidewalls, andwherein at least one of said sidewalls comprises means for holding saidshell.
 13. The yarn brake of claim 12, wherein said means for holdingsaid shell comprises a hole in the at least one said sidewalls andreleasable fasteners engaging said hole.
 14. The yarn brake of claim 12,further comprising an adjusting screw that engages said fixed frame andthat moves said shell relative to said fixed frame.
 15. The yarn brakeof claim 9, further comprising a third yarn guide element in thestraight yarn path and between said arms of said generally U-shapedbracket.
 16. The yarn brake of claim 15, further comprising a generallyU-shaped support attached to said fixed frame and holding a downstreamone of said first and second yarn guide elements, said third yarn guideelement being on a column projecting into said generally U-shapedsupport.
 17. The yarn brake of claim 16, wherein said downstream one ofsaid first and second yarn guide elements comprises an annular yarneyelet, and wherein said generally U-shaped support comprises a roundedcover part that carries said annular yarn eyelet.